Identification of local anisotropy and determination of principal axes is addressed through different methods that are designed to be tolerant to the non-smooth character of images on the pixel scale. These different tools are validated on various examples, and their performances are compared. The most powerful, robust and accurate method consists in computing the curvature tensor of the auto-correlation function of regularized images using fast Fourier transforms. Key words: Texture analysis, padding, orientation, fibrous material. PACS: